Hybrid electric vehicles (HEVs) and electric vehicles (EVs) provide improved fuel economy and reduced air emissions over conventional vehicles. The performance of HEVs and EVs depend on energy storage systems such as batteries. Battery performance influences, for example, acceleration, fuel economy, and charge acceptance during recovery from regenerative braking. As the cost of the batteries, durability, and life-cycle affect the cost and reliability of a vehicle using the batteries for vehicular operation, parameters that affect the efficiency of the batteries may have to be optimized to achieve optimized vehicular performance.
It is known that temperature has an influence over battery performance. Battery modules carrying batteries are preferred to operate within an optimum temperature range that is suitable for a particular electrochemical pair. For example, the desired operating temperature for a lead acid battery is 25° C. to 45° C. Battery modules may also have to be operated at uniform temperatures as uneven temperature distribution may result in varied charge-discharge behavior. Such varied charge-discharge behavior may lead to electrically unbalanced modules and reduced battery performance.
HEVs may be less reliable in northern latitudes due to cold temperature constraints imposed on the batteries carried by the HEVs. Lithium ion batteries have been a candidate for use in HEVs, and such batteries have optimum performance when operating from 0–40° C. Below 0° C., power output of the batteries diminishes and the effect of temperature becomes more severe as the level of discharge increases. Conversely, as temperatures exceed above 40° C., detrimental cathode corrosion and other irreversible reactions may occur resulting in shortened battery life.
Accordingly, a battery thermal management system (TMS) is needed to achieve desired and reliable performance in varied climatic conditions while minimizing temperature excursions outside a desired temperature range.